Zigzag carbon electric resister.



J. THOMSON.

zlGzAG CARBON ELECTRIC RESISTEH.

APPLICATION FILED APR.I6.19I8.

Patented Mar. 25,1919.

ILII l E INVENTOH Br f /f/fATToH/vfrs L invented certain new and useful Improve- Carbon Electric Resistors,

JOHN THOMSON, OF NEW YOIK,'N. Y.-

ZIGZAG- CARBON ELECTRIC Specication of Letters Patent. i

Patented Mar. 2 5, 1919.

Application led April 16, 1F18. Serial No. 228,908.

To all whom it may concern:

Be it known that I, JOHN THOMSON, a citizen of the United States, and a resident of the borough of Manhattan, city of New York, county'and State of vNew York, have ments in Zigza of which the fo owing is a specification, reference being. made to the accompanying drawings, forming a part thereof.

This invention relates to carbon resisters as employed in electric furnaces,'usual1y in the form of rods, slabs or plates', in which a plurality of staggered slots are cut whereby to produce a lengthy sinuous circuit of restricted. erom-section. A resister of this type is designated in common parlance a zi -zag resister.

object of the present invention is to render the carbon element immune to oxidizati'o'nfor air-burni and to restore or maintain the stability o the slotted member so as to ap roximately equal that of the original rod, s ab or plate from which it was formed.

In the accompanaying drawing forming a part of this specification there appear diagrammatic illustrations which denote how the invention may be realized. In said drawing,

Figure l is a plan view, partially broken away, of a zig-zag plate resister, such as might be used in various types of electric furnaces. f

Fig. 2 is a side view thereof.

Fig. 3 is a transverse section through any ofthe slotted portions of the resister. It is a view taken as on the plane indicated by the line 3-3 of Fig. 1 looking in the direction of the arrows.

Fig. 4 is a transverse section through the solid portions of the resister; or, in other words, is a transverse view taken between the slotted portions of the resister. This fi ure is a view taken as on the plane indicate by the line 4-4 'of Fig. 1 looking in the direction of the arrows. l

Fig.. 5 is a transverse section through a slottedv portion of a resister and indicates a modification in the detail 0f carrying the invention into useful effect.

It is in accord with the facts to state that.

resisters of the type herein referred to possess a unique efiiciency for transformin large units of power into heat and thence ra iating or giving off said heat at high maintainable temperatures. The members from which they are made can be formedby die-squirting; viz., by squirting a mixture containing carbon through a die to forma longitudinally extendin member, and either amorphous or grapitized carbon may be used.

A resister made from a member thus formed has the utmost uniformity as to density 'and resistivity. But in order to employ such resisters in the arts, except in a few special instances, they must be placed within closed casings or chambers from which air is wholl excluded, else they will be quickly oxidize Moreover,` spacious chambers or protective casings present a more or less formidable obstruction to the rapid transfer therethrough of radiant heat. Then, too, the transverse l stability of the slotted resister is manifestly much diminished over that of the member from which it 'was formed; so much so, in fact, that the slotted resisters usually require to be supported between their terminals.

Accordin to the present invention the objectionable eatures are obv'iated and certain requirements are taken care of by filling the slots of thepresister and by coating the surfaces of the resister, or such portions thereof asvmay be necessary, with a material, or mixture of materials, possessing the followingr characteristics 5 he material or materials should have a coefficient of expansion and contraction nearly identical to that of the carbon of the resister. The material or materials should be of a character either to adhere or lie in close proximity to the carbon of the resister. The material or materials should be of a character which is a relatively good conductor of heat but a relatively good non-conductor of electricity, f and it or they should be non-reactive with carbon and immune to oxidization.

The materials which have been ascertained as most fully meeting the requirements just specified are fused aluminum oxid and silicon carbid in its crystalline form, either of which may be mixed, to some minimum extent, with a binding substance of somewhat lesser refractability, such, say, as crcibleclays slightly moistened, as by water, silicate of soda, etc., whereby the mixture approximates the consistency of putty or a, rather stif paste or cement. All such mixnati tures, as when used formaking crucibles, retorts or mufiles, if the very best results are to be attained, must be subjected 'to along period of low temperature curing and thereafter be baked in kilns, usually in an oxidizing atmosphere, yet it is seldom that the final kiln-temperature is as high as that to` which the article is ultimately subjected.,

Referrin to the drawings, B represents a carbon p ate in which a plurality of altery slots C, have beenv formed, whereby the e ectric circuit becomes a zig-zag path, as. shown by the line D, and thence passes to the source of energy E.

The protective coating F, having `the physical characteristics already set forth, is then applied to such portions of the resister-surface as may be desired-in Figs. 1 and 2 the ends are shown exposed,l as for connection with terminals-and the material is also packed into the slots, completely filling them, see Fig. 3. The next preferable step in the procedure is to somewhat dry the coating, as in a warm room or japanning oven. The final step is to place the' esister in a power-circuit capable-of voltarge adjustment vand progressively heating it, carrying the temperature up to a point which shall be somewhat higher than that to which the resister is to be subjected in service. In this wise, the final curing temperature is developed from Within the coating, the mois-l ture being expelled instead of 'being Withdrawn, as in a kiln. As a consequence of this the effectiveness of the curing is enhanced and the period of' time necessary for the treatment is much diminished. But the final curing of the sheathing, or envelop, needs sister becomes substantially equal to that of the originalplate, before the slots were formed; moreover, the material in the slots serves as very effective anchorages for the coating on the surfaces. f

It is advantageous to remove all sharp edges frofn the carbon plate, leaving fillets .or rounds, as ha Normally, the electric resistance of a filled-in resister would be less than if the slots were open. However, this condition is satisfactorily adjustable to the requirements .of practice by forming wider slots than would be necessary were they to remain unfilled; or, again, the slots may be filled with dry, unalloyed granular material, as

8 Fig. 5, tamped into place before the cement is applied. Thus, the electric resistance across the slots is increased. over -that of a more solid substance, yet the broken particles in granular'form, as sand, or in powdered form serve to support the sides of the slots and maintain the stability'of the structure. To justify the foregoing, it may be here stated, based upon various tests and performances, that, as the electromotiveforce from any single limb of the zig-zags crosswise of a slot to its contiguous member rarely exceeds from say, 1.5 to 2.5 volts, the drop in resistance, as a whole, is virtually negli- 'gible Hence, it is both adequate and nfeasible, and in certain instances even more convenient, to first tamp or mold the material in the form of thin plates and then insert them in the slots, either dry orwith a coat-- ingof cement to cause them to adhere. In this wise, even if an over-all coating or sheathing is not applied, the stability of the resister, especially when .heated to a high temperature, is greatly increased.

In furnaces for melting non-ferrous metals, for heating steel billets to be forged, for refining zinc by redistillation and for various smelting operations the highest temperature required in the resister itself needv not exceed, say 1500 degrees C. to 1700'degrees C., which is well within the capacity of a thinl sheathing of aluminum oxid or' silicon carbid to withstand withoutV softening or setting-up a reaction with the carbon. The capacity of the carbon to transfer heat by conduction through such a shield and thence to the charge by radiation is theoretically diminished; but in a practical sense the amount. of this diminution is a negligible quantity.

An important advantage of this inventionl is comprehended in thefollowing:

The invention transposes 4a device of ratherv delicate construction of limited' en'- .durance and' of restricted applicability into `one which is robust in construction, is of long endurance and has a broad or well-nigh universal applicability.

What I claim is 1. An electric, carbon, zig-zag resister whose slots'are filled and whose exterior sury faces, or a major ortion thereof, are coated with material re atively'non-conductive to electricity, immune to oxidization and nonreactive with carbon.

whose slots are Afilled with dry granular mamajor portion thereof, are `coated with the same material in the form .of a baked cement, the said material beingrelatively non-conductive to electricity, immune to oxidization and non-reactive w1th carbon. f

3. An electric, carbon, zig-zag resister, whose slots are filled-and whosefsurfaces, or a major ortion thereof, are coated with ma- 2. An electrlc, carbon, zig-zag resister r terial w ichl is relatively non-conductive to electricity, immune to oxidization and nonreactive with carbon, the said material being cured or baked in place by heat developed in the resister.

4:. An electric, carbon, Zig-zag 'resister the Slots of which are filled with relatively, electrically non-conducting material.

5. An electric, carbon, zlg-zag resister the slots of Which are filled With material relatively non-conductive to electricity and immune to oxidization.

6. An electric, carbon, zig-zag resister the slots of which are filled With material that is relatively non-conductive to electricity, the exterior of said resister or a major portion thereof being coated with material Which is relatively non-conductive to electricity and immune to oxidization.

7.v An electric carbon, zig-Zag resister the slots of which are filled with material relatively non-conductive to electricity and which resister is surrounded substantially throughout its length by a coating of material relatively non-conductive to electricity,

immune to oxidization and n0n-reactive with carbon.

8. An electric, carbon, zig-zag resister the slots of which have therein filling material and which resister has a surrounding coatin that is relatively non-conductive to electrlcity, that is immune to oxidization and that is Itonreactive with carbon.

9. An electric, carbon resister Athe slots `of which are filled with fused aluminum oxid and silicon carbid in crystalline form.

slots of which are filled with material that 1s relatively non-conductive to electricity and which resister is surrounded by a coating of ers, the method which comprises squirting a mixture containing carbon, through a die in order to form a longitudinally extending member, providing slots in said member in a manner that there results a zig-Zag member, filling said slots with relatively electricall non-conducting material and. surrounding said zig-zag member with a wet or moist material, partially drying moist material thus added, and finally passing electrical current through said zig-zag member and progressively heating it until the temperature reaches a point higher than that at which the resulting resister is to be used.

l2. The method comprised in filling the slots of a carbon, zig-zag resister with material relatively non-conductive to electricity, non-oxidizable and non-reactive with carbon; enveloping the said resister With a sheathing which is also formed of material Vrelatively non-conductive to electricity, nonoxidizable and non-reactive with carbon and curin the said sheathing in place.

This specification signed and witnessed this 13th day of April, A. D. 1918.

' JOHN THOMSON. Signed in the presence of- J. R. AGNEW, JOSEPH H. STEHN. 

